Comparison of the INNOVA visual acuity system stereotest with the Frisby-Davis 2 stereotest for the evaluation of distance stereoacuity

Purpose: Distance stereo acuity has been shown to be useful in monitoring conditions such as control of intermittent strabismus. The Frisby Davis distance (FD2) stereotest has been shown to be reliable and is felt to be the gold standard in England. The device however is not widely available in the United States or Canada and is not automated. This study compares the Innova distance stereoacuity test with the Frisby Davis distance (FD2) stereotest. Methods: Twenty-seven patients with normal acuity and a normal ophthalmology exam were evaluated. Prior to dilation all patients had an Innova distance stereoacuity test and FD2 test. Both the Innova distance stereoacuity test and the FD2 test were performed at ten feet. The results of the tests were compared using Bland-Altman plot analysis. Results: The INNOVA system tended to underestimate distance stereoacuity by approximately 30 arc seconds compared to the FD2 test. If the INNOVA results were corrected by this amount, then there was a good correlation between the INNOVA results and the FD2. Conclusion: The Innova distance stereoacuity test underestimates stereopsis by approximately 30 arc seconds but does so with sufficient consistency that it may serve as an acceptable method of measuring distance stereoacuity. This study is the first that has correlated the Innova stereoacuity test with the FD2.